Protective system for electric circuits



July 25, 1933. J. STOECKLIN PROTECTIVE SYSTEM FOR ELECTRIC CIRCUITS Filed Jan. 22, 1951 Patented July 2 5, 1933 UNITED STATES PATENT OFFICE JOSEF STOECKLIN, OF ZURICH, SWITZERLAND, ASSIGNOR TO AKTIENGESELLSCHAFT BROWN BOVERI 8a CIE, OF BADEN, SWITZERLAND, A JOINT STOCK COMPANY OF SWITZERLAND PROTECTIVE SYSTEM FOR ELECTRIC CIRCUITS Application filed January 22, 1931, Serial No.

It has already been proposed for protectingthree-phase lines to introduce time-delay ohnimet'ric relays only in two phases with the object of saving relays and current transformers and thus reduce the size of the protective devices as far as possible. WVhen, however, this limiting to two relays is etfected without the adoption of additional measures/the protective value of the ar rangement will be very detrimentally atfeeted, for instance in the case of a twophase short-circuit.

.According to the invention the full effectiveness of the protection in the case of twophase short-circuits between any phases and in the case of three-phase short-circuits may be secured by replacing the missing timedelay ohmmetric relay in the third phase by a simple, momentarily-acting excess current relay which, coacting with the two time-delay voh rnmetric relays, either blocks the latter or reverses their voltage circuits.

I In the accompanying drawing a constructional example of the invention is schematically illustrated. To the two phase conductors RT of the network RST there are connected by way of two current transformers a and two voltage transformers 1) two time-delay ohmmetric selective relays r and t which may consist of the cross-coil time-delay release type (such as disclosed in German Patent 408,131) with the current coils e and the voltage coil and of the time-delay coil 9*, which actuate the contact memhere it and i respectively. In the common return lead a of the coilse, 9, through which current flows, there is introduced the coil 8 of an overload relay with three contact menibers m, n, 0. When in consequence of an overload in the time-delay coil g, the relays r or t respond and run down till they close their contact h and a respectively, whereby the circuit-breaking electro-magnet g of the main switch a is energized from the battery p and the switch 0 is opened. On the relay t esponding, the time'del-ay actuating co1l g1 of the relay 1'. is momentarily short-circuited by the closure- 0f contacts is responslve to' energization of the time-delay coil g of relay t. On the overload relay 8 responding,

510,567, and in Germany January 23, 1930.

the short-circuit 01" the time-delay coil 9 of relay If is opened by the contact on and at the same time the voltage coil f of the relay achanged over by the contacts a and 0 from the voltage RT to the voltage RS. The voltage coil of the relay t is permanently connected to the voltage ST.

The manner in which the arrangement operates in the four different short-circuit cases shall now be explained.

1. On a short-circuit occurring between the phase conductors R and T, the current coils e of the two relays r and 3 will receive an overload and also the time-delay coil 9 of the relay 1, while that of the relay t is short-circuited by the contact m. Ofthe voltage coils f of the two relays that of the relay '2 which is connected by way of the contact a to the phases RT is practically unenergized, owing to the short-circuit, while that of the relay t, which is connected to the phases ST, is normally energized. The relay 8 does not carry an overload and therefore does not respond. Owing to simultaneous overload and low tension voltage at the cross-coil member, the relay 9" completes its motion and by closing its contact It causes the switch 0 to open.

2. On a short-circuit occurring between the lines R and S, the overload current flows through the coils e and g of the relay 9 and through the relay 8, while only the normal current flows through the relay 1;. The two voltage coils at first receive nor mal voltage from the sound phases RT and ST. Through the relay .9 responding, the voltage coil of the relay 1" is momentarily disconnected from the voltage RT and connected over the contact 0 to the broken down voltage RS. The cross-coil member 6, f of the relay 1 is thus again caused to operate and by closing its contact it opens the main switch 0.

3. On a shortcircuit occurring between the phases S and T the current coils e of the relay 7 receive normal current, while the coil 0 of the relay 6 and the relay .9 receive an overload current. At first only the latter relay 8 responds and opens the short-circuit of the coil 9 of the relay t, the voltage coil of which is connected to the short-circuit voltage ST. The relay t will now respond and continue to operate until its contact 2' opens the switch 0.

4. A shortcircuit between two or all three phases RST will first result in the two relays 1" and s responding. As, through the opening of the contact m, the time-delay actuating coil 9 of the relay t will also receive short-circuit current, this relay will respond and immediately short circuits the time-delay actuating coil 9 of the relay 7" by means of the contact k so that the relay 1" will return into its inoperative position and remain blocked, although its cross-coil member is fed with overload current and low tension voltage. The relay t, however, will continue to operate until the switch 0 is released by the contact In this way the object is realized of satisfactorily dealing with the various cases of short-circuit in a three-phase network by means of two selective relays, two current transformers, two voltage transformers and an ordinary overload relay.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. In a protective system for electric circuits, a polyphase line, a switch means operable to interrupt said line, a first time-delay ohmmetric relay connected to be responsive to a fault connection in one phase of said line, a second time-delay ohmmetric relay connected to be responsive to a fault connection in another phase of said line, and a control relay having means normally rendering the said second relay inoperative, the said control relay being responsive to the occurrence of a fault connection in the said one and the said another phase of said line to render operative the said second relay up'di the occurrence of a fault connection in the" said another phase of said line and to connect the voltage responsive element of the said first relay to be responsive to the voltage of the said one phase of said line upon the occurrence of a fault connection therein, and means actuated responsive to the actuation of the said second relay operable to render the said first relay inoperative, the operation of either said first relay or the said second relay being effective to cause circuit interruption actuation of the said switch means.

2. In a protective system for electric circuits, a polyphase line, a switch means operable to interrupt said line, a first time-delay ohmmetric relay connected to be selectively responsive to a fault connection in a one phase and in a second phase of'said line, a seeond time-delay ohmmetric relay connected to be selectively responsive to a fault connection in a third phase on a fault connection between any two or all of said phases of said line, and a control relay having means normally rendering inoperative the said second relay, the said control relay being responsive to a fault connection in the said second and the said third phases of said line to render operative the said second relay upon the occurrence of a fault connection in said third phase or a fault connection between any two or all phases of said line, and to render the said first relay responsive to a fault connection in the said second phase of said line, and the said second relay having means effective upon operation thereof to render inoperative the said first relay, the operation of either the said first relay or the said second relay being effective to cause circuit interrupting actuation of the said switch means.

In a protective system for electric circuits, a polyphase line, a switch means opcrable to interrupt said line, a first relay comprising an element connected to be selectively actuated responsive to the ratio of g in a first phase and a second phase of said line upon the occurrence of a fault connection therein, and a time-delay element connected to be concurrently actuated responsive to abnormal flow of current in the said phases of said line, a second relay having an element connected to be selectively actuated responsive to the ratio of in a third phase of said line upon the occurrence of a fault connection therein and upon the'occurrence of a fault connection between any two or all phases of said line, and a time-delay element connected to be concurrently actuated responsive to abnormal flow of current in the last said phases of said line, the said timedelay element of the said second relay having means operable to render inoperative the time-delay element of the said first relay upon the operative actuation of the said second relay, and a control relay connected to be actuated responsive to abnormal flow of current in the said second and third phases of said line, the said control relay having elements normally operative to prevent operative actuation of the time-delay element of the second said relay and to render the said first relay responsive to a fault-connection in thesaid one phase of said line only, the said elements being operative upon actuation of said control relay to render operative the time-delay element of the said second relay and to render the said first relay responsive to a fault connection in the said second phase of said line, the actuation of either the said first relay or the said second relay being operative to cause circuit interruption actuation of the said switch means.

4. In a protective system for electric cirs'uits, a polyphase line a switch means operable to interrupt said line, a pair of relays each comprising an ohmmetric element having a voltage responsive actuating coil and a current responsive actuating coil, and a time delay element having a current responsive actuating coil, and a control relay having a current responsive actuating coil, the said voltage and current responsive coils of one of said pair of relays being connected to be selectively actuated responsive to a a fault connecting in a first and a second mally render the said other of said relays inoperative and to connect the said voltage coil of the said one relay of said pair of relays to be energized responsive to the voltage of the said one phase of said line, the said means being operative upon the said energization of the coil of the control relay to render the said another of said pair of relays operative and to connect the said voltage coil of the said one of said pair of relays to be responsive to the voltage of the said second phase of said line, the time-delay element of the said other of said pair of relays having means operable to render in operative the time-delay element of the said one of said pair of relays upon the actuation of the time-delay element of the said other relay, the actuation of either of said pair of relays being operative to cause circuit interruption actuation of the said switch means.

J ()SEF STOECKLIN. 

